Research

14 pages, 7779 KiB

Open AccessArticle

Thermal Shock Behavior of Si₃N₄/BN Fibrous Monolithic Ceramics

by Qingqing Chen, Yuan Zhang, Yu Zhou, Daxin Li and Guobing Ying

Materials 2023, 16(19), 6377; https://doi.org/10.3390/ma16196377 - 24 Sep 2023

Viewed by 838

To develop materials suitable for aerospace applications, silicon nitride/boron nitride (Si

_{3}

N

_{4}

/BN) fibrous monolithic ceramics with varying BN contents were prepared. Employing analytical techniques such as XRD and SEM, coupled with mechanical testing equipment, the influence of BN concentration on [...] Read more.

To develop materials suitable for aerospace applications, silicon nitride/boron nitride (Si

_{3}

N

_{4}

/BN) fibrous monolithic ceramics with varying BN contents were prepared. Employing analytical techniques such as XRD and SEM, coupled with mechanical testing equipment, the influence of BN concentration on the thermal shock resistance of Si

_{3}

N

_{4}

/BN fibrous monolithic ceramics was assessed. When the thermal shock differential is less than 800 °C, its residual flexural strength gradually decreases as the thermal shock differential increases. Conversely, when the differential exceeds 1000 °C, the residual flexural strength of the material increases. The residual strength of all samples reached its peak after undergoing a thermal shock assessment at a 1500 °C differential. When the BN mass fraction is 5 wt.%, the residual strength after a thermal shock at a temperature difference of 1500 °C is 387 ± 19 MPa, which is 124% higher than the original strength of the sample that did not undergo thermal shock (25 °C, 311 ± 18 MPa). The oxide layer formed on the thermal shock surface played a role in bridging defects introduced during material surface processing. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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15 pages, 6302 KiB

Open AccessEditor’s ChoiceArticle

Advanced Fabrication Method and Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics

by Qingqing Chen, Yuan Zhang, Liuxin Chao, Ningning Dong, Yu Zhou and Guobing Ying

Materials 2023, 16(18), 6130; https://doi.org/10.3390/ma16186130 - 08 Sep 2023

Viewed by 842

Abstract

Silicon nitride ceramics are regarded as a promising material for high-temperature structural applications due to their remarkable characteristics, including high strength, hardness, thermal conductivity, low dielectric properties, and resistance to creep at elevated temperatures. However, their susceptibility to catastrophic fracture at high temperatures [...] Read more.

Silicon nitride ceramics are regarded as a promising material for high-temperature structural applications due to their remarkable characteristics, including high strength, hardness, thermal conductivity, low dielectric properties, and resistance to creep at elevated temperatures. However, their susceptibility to catastrophic fracture at high temperatures remains a concern. Herein, Si₃N₄/BN fibrous monolithic ceramics have been successfully prepared by employing wet-spinning and hot-pressing techniques. We delved into the design and optimization of the spinning slurry and examined how the Si₃N₄/BN fiber diameter affects the ceramics’ microstructure and mechanical properties. The spinning slurry exhibited exceptional stability and spinnability. Decreasing the fiber diameter contributed to material densification and improved mechanical properties. Notably, when the fiber diameter is 0.9 mm, the fabricated Si₃N₄/BN fibrous monolithic ceramics demonstrate a carbon content of 0.82%, a three-point bending strength of 357 ± 24 MPa, and a fracture toughness of 8.8 ± 0.36 MPa·m^1/2. This investigation offers valuable insights into producing high-performance Si₃N₄/BN composite ceramics utilizing hot-pressing technology. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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14 pages, 6093 KiB

Open AccessEditor’s ChoiceArticle

Study of the Mineralogical Composition of an Alumina–Silica Binder System Formed by the Sol–Gel Method

by Lenka Nevřivová and David Zemánek

Materials 2023, 16(15), 5466; https://doi.org/10.3390/ma16155466 - 04 Aug 2023

Cited by 1 | Viewed by 819

Abstract

Colloidal bonds are realized by sol–gel technology. The binder system of the refractory castable belongs to the Al₂O₃–SiO₂ binary diagram. Mullite is the most thermally stable mineral in this system. This work was motivated by an attempt to [...] Read more.

Colloidal bonds are realized by sol–gel technology. The binder system of the refractory castable belongs to the Al₂O₃–SiO₂ binary diagram. Mullite is the most thermally stable mineral in this system. This work was motivated by an attempt to maximize the mullite content in the NCC binder system, because a high content of mullite is a guarantee of the long service life of refractories. Initially, the mineralogical composition of the pure gel was tested after drying and firing at temperatures between 1000 °C and 1600 °C. The behavior of the gel during drying was described. Subsequently, a method of minimizing gel shrinkage during drying was sought. To this aim, fine fillers (microfillers) of alumina and silica were tested. In particular, the reactivity of the microfillers, the ability of the microfillers to react with the sol to form mullite, and the drying shrinkage of the microfiller-doped gel were evaluated. The study showed that the least suitable source of Al₂O₃ in terms of its reactivity is tabular corundum, which produces the lowest amount of mullite. The internal structure of the prepared binder system when using different microfillers was described. Based on the results from the second stage of the work, several complete matrixes of the binder system were designed and the degree of their mullitization at different firing temperatures was studied. During this stage, it was shown that the degree of mullitization of the binder system depends mainly on the microsilica content. In the binder system, the maximum mullite content recorded was 76%. The effect of amorphous SiO₂ on the bulk density and internal structure of the binder system was also described. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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14 pages, 6180 KiB

Open AccessArticle

Effects of Ti on the Microstructural Evolution and Mechanical Property of the SiBCN-Ti Composite Ceramics

by Hao Peng, Daxin Li, Zhihua Yang, Wenjiu Duan, Dechang Jia and Yu Zhou

Materials 2023, 16(9), 3560; https://doi.org/10.3390/ma16093560 - 06 May 2023

Cited by 2 | Viewed by 1195

Abstract

In this study, amorphous + nanocrystalline Ti-BN mixed powders were obtained through first-step mechanical alloying; subsequently, almost completely amorphous SiBCN-Ti mixed powders were achieved in the second-step milling. The SiBCN-Ti bulk ceramics were consolidated through hot pressing sintering at 1900 °C/60 MPa/30 min, [...] Read more.

In this study, amorphous + nanocrystalline Ti-BN mixed powders were obtained through first-step mechanical alloying; subsequently, almost completely amorphous SiBCN-Ti mixed powders were achieved in the second-step milling. The SiBCN-Ti bulk ceramics were consolidated through hot pressing sintering at 1900 °C/60 MPa/30 min, and the microstructural evolution and mechanical properties of the as-sintered composite ceramics were investigated using SEM, XRD, and TEM techniques. The as-sintered SiBCN-Ti bulk ceramics consisted of substantial nanosized BN(C), SiC, and Ti(C, N) with a small amount of Si₂N₂O and TiB₂. The crystallized BN(C) enwrapped both SiC and Ti(C, N), thus effectively inhibiting the rapid growth of SiC and Ti(C, N). The sizes of SiC were ~70 nm, while the sizes of Ti(C, N) were below 30 nm, and the sizes of Si₂N₂O were over 100 nm. The SiBCN-20 wt.% Ti bulk ceramics obtained the highest flexural strength of 394.0 ± 19.0 MPa; however, the SiBCN-30 wt.% Ti bulk ceramics exhibited the optimized fracture toughness of 3.95 ± 0.21 GPa·cm^1/2, Vickers hardness of 4.7 ± 0.27 GPa, Young’s modulus of 184.2 ± 8.2 GPa, and a bulk density of 2.85 g/cm³. The addition of metal Ti into a SiBCN ceramic matrix seems to be an effective strategy for microstructure optimization and the tuning of mechanical properties, thus providing design ideas for further research regarding this family of ceramic materials. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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15 pages, 3659 KiB

Open AccessArticle

Preparation of In Situ Growth Multiscale β-Sialon Grain-Reinforced Al₂O₃-Based Composite Ceramic Tool Materials

by Jian Zhu, Yunna Xue, Xiaolan Bai, Xuehui Shen, Jianqun He, Yu Zhang and Anhai Li

Materials 2023, 16(6), 2333; https://doi.org/10.3390/ma16062333 - 14 Mar 2023

Cited by 1 | Viewed by 1059

Abstract

A kind of multiscale β-sialon grain-reinforced Al₂O₃ matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, β-sialon (molecular formula: Si₄Al₂O₂N₆) was synthesized in situ by a hot-pressing [...] Read more.

A kind of multiscale β-sialon grain-reinforced Al₂O₃ matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, β-sialon (molecular formula: Si₄Al₂O₂N₆) was synthesized in situ by a hot-pressing and solid-solution reaction process. A total of six samples were prepared at varying sintering temperatures and holding times under vacuum conditions. The solid solution reaction mechanism of β-sialon, the phase composition, mechanical properties, microstructure, and strengthening and toughening mechanisms of the composite ASN were investigated. As a result, within the experimental parameters, an optimal ASN tool material was obtained under a pressure of 32 MPa and at a temperature of 1550 °C for 20 min. The tested mechanical properties of the optimal sample were as follows: flexural strength 997 ± 59 MPa, fracture toughness 6.4 ± 0.3 MPa·m^1/2, Vickers hardness 18.2 ± 0.4 GPa, and relative density 98.1 ± 0.2%. According to crystal defect theory, the solid solution reaction mechanism of in-situ-synthesized β-sialon in an Al₂O₃ matrix involves a double mechanism of unequivalence (or hetero-valence) and interstitial filling. The multiscale β-sialon grains mainly consisted of four grains, which were elongated β-sialon grains with a diameter of 0.3–0.4 μm and an aspect ratio of 6–9, elongated β-sialon grains with a diameter of 70 nm and an aspect ratio of 10, β-sialon whiskers with a diameter of 0.2 μm and an aspect ratio of 12–15, and intragranular β-sialon whiskers with a diameter of 70 nm. The mechanical properties were improved due to strengthening and toughening mechanisms, such as mixed structure mode (intergranular and transgranular), elongated grain pullout, interface bonding, crack reflection, pinning, and bridging. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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13 pages, 4413 KiB

Open AccessArticle

A Novel Process for the Containment of SO₂ Emissions from Class C Fly Ash in the Fired Materials by Haüyne Formation

by Radomir Sokolar and Martin Nguyen

Materials 2022, 15(19), 6701; https://doi.org/10.3390/ma15196701 - 27 Sep 2022

Viewed by 909

Abstract

Class C fly ash has been receiving increasing attention due to the gradual transition of thermal power plants all over the world to the fluidized bed combustion technology with sulfur dioxide emissions capture. This research investigates the utilization of class C fly ash [...] Read more.

Class C fly ash has been receiving increasing attention due to the gradual transition of thermal power plants all over the world to the fluidized bed combustion technology with sulfur dioxide emissions capture. This research investigates the utilization of class C fly ash in fired ceramic materials with simultaneous efficient and novel containment of sulfur dioxide emissions in the flue gas during firing. A number of experiments were conducted by addition of sodium water glass with different molar ratios of SiO₂:Na₂O, sodium carbonate, and different ratios of sodium carbonate to water glass to the class C fly ash to examine the optimal combination and quantity for the creation and formation of the mineral phase haüyne which resulted in reduction and containment of SO₂ emissions. Results revealed that a 12% dose of sodium water glass with a low molar ratio of 1.7 (SiO₂:Na₂O) combined with class C fly ash was more effective in the formation of haüyne and the resulting decrease of SO₂ in the flue gas was more substantial. The newly formed mineral phase haüyne was identified by an X-ray diffraction analysis and scanning electron microscopy with energy dispersive X-ray spectroscopy. Outcomes reveal a potential for utilization of class C fly ash in the fired materials by containment of sulfur dioxide into their structure. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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21 pages, 42756 KiB

Open AccessArticle

Study of Wettability and Solderability of SiC Ceramics with Ni by Use of Sn-Sb-Ti Solder by Heating with Electron Beam in Vacuum

by Roman Kolenak, Igor Kostolny, Jaromir Drapala, Jan Urminsky, Alexej Pluhar, Paulina Babincova and Daniel Drimal

Materials 2022, 15(15), 5301; https://doi.org/10.3390/ma15155301 - 01 Aug 2022

Cited by 1 | Viewed by 1238

Abstract

The aim of this research was to study the wettability and solderability of SiC ceramics by the use of an active solder of the type Sn5Sb3Ti in a vacuum by electron beam heating. This solder exerts a narrow melting interval, and only one [...] Read more.

The aim of this research was to study the wettability and solderability of SiC ceramics by the use of an active solder of the type Sn5Sb3Ti in a vacuum by electron beam heating. This solder exerts a narrow melting interval, and only one thermal effect, a peritectic reaction, was observed. The liquidus temperature of the solder is approximately 243 °C. The solder consists of a tin matrix where the Ti₆(Sb,Sn)₅ and TiSbSn phases are precipitated. The solder wettability on a SiC substrate decreases with decreasing soldering temperature. The best wetting angle of 33° was obtained in a vacuum at the temperature of 950 °C. The bond between the SiC ceramics and the solder was formed due to the interaction of Ti and Ni with silicon contained in the SiC ceramics. The formation of new TiSi₂ and Ti₃Ni₅Si₆ phases, which form the reaction layer and thus ensure the bond formation, was observed. The bond with Ni is formed due to the solubility of Ni in the tin solder. Two phases, namely the Ni₃Sn₂ and Ni₃Sn phases, were identified in the transition zone of the Ni/Sn5Sb3Ti joint. The highest shear strength, around 40 MPa, was attained at the soldering temperature of 850 °C. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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12 pages, 4625 KiB

Open AccessArticle

Properties of Ceramic Coating on Heating Surface of Waste Incineration Boiler Prepared by Slurry Method

by Zengzhi Wei, Lijun Wu and Xingyuan Liang

Materials 2022, 15(13), 4574; https://doi.org/10.3390/ma15134574 - 29 Jun 2022

Cited by 2 | Viewed by 1775

Abstract

In order to alleviate the problem of high-temperature fly ash corrosion and slag on the heating surface of a high-parameter waste incinerator, a ceramic coating material that can be prepared in situ on the heating surface by the slurry method was studied. The [...] Read more.

In order to alleviate the problem of high-temperature fly ash corrosion and slag on the heating surface of a high-parameter waste incinerator, a ceramic coating material that can be prepared in situ on the heating surface by the slurry method was studied. The ceramic coating can be formed by sintering at a lower temperature of 750 °C. Its surface and profile are very dense, and the porosity is less than 1%. The mechanical properties test results show that the ceramic coating can withstand 60 cycles of water-cooled thermal shock at 700 °C, and the bonding strength is 25.14 ± 2.21 MPa. It will not fall off in a large area when subjected to pressure load, and it has a certain degree of processable plasticity. High-temperature wettability experiments show that the ceramic coating has lower liquid-bridge force, smaller adhesion area, and shorter fouling cycle for molten corrosive fouling, and potential self-cleaning properties. Its practical mechanical properties make the coating valuable for production applications and meet expectations, and excellent antifouling properties to reduce average fouling thermal resistance and corrosion. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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